Monocarboxylate transporters facilitate succinate uptake into brown adipocytes.

Uptake of circulating succinate by brown adipose tissue (BAT) and beige fat elevates whole-body energy expenditure, counteracts obesity and antagonizes systemic tissue inflammation in mice. The plasma membrane transporters that facilitate succinate uptake in these adipocytes remain undefined. Here we elucidate a mechanism underlying succinate import into BAT via monocarboxylate transporters (MCTs). We show that succinate transport is strongly dependent on the proportion that is present in the monocarboxylate form. MCTs facilitate monocarboxylate succinate uptake, which is promoted by alkalinization of the cytosol driven by adrenoreceptor stimulation. In brown adipocytes, we show that MCT1 primarily facilitates succinate import. In male mice, we show that both acute pharmacological inhibition of MCT1 and congenital depletion of MCT1 decrease succinate uptake into BAT and consequent catabolism. In sum, we define a mechanism of succinate uptake in BAT that underlies its protective activity in mouse models of metabolic disease.

Peripheral Administration of Norepinephrine: A Prospective Observational Study.

BACKGROUND: Historically, norepinephrine has been administered through a central venous catheter (CVC) because of concerns about the risk of ischemic tissue injury if extravasation from a peripheral IV catheter (PIVC) occurs. Recently, several reports have suggested that peripheral administration of norepinephrine may be safe. RESEARCH QUESTION: Can a protocol for peripheral norepinephrine administration safely reduce the number of days a CVC is in use and frequency of CVC placement? STUDY DESIGN AND METHODS: This was a prospective observational cohort study conducted in the medical ICU at a quaternary care academic medical center. A protocol for peripheral norepinephrine administration was developed and implemented in the medical ICU at the study site. The protocol was recommended for use in patients who met prespecified criteria, but was used at the treating clinician's discretion. All adult patients admitted to the medical ICU receiving norepinephrine through a PIVC from February 2019 through June 2021 were included. RESULTS: The primary outcome was the number of days of CVC use that were avoided per patient, and the secondary safety outcomes included the incidence of extravasation events. Six hundred thirty-five patients received peripherally administered norepinephrine. The median number of CVC days avoided per patient was 1 (interquartile range, 0-2 days per patient). Of the 603 patients who received norepinephrine peripherally as the first norepinephrine exposure, 311 patients (51.6%) never required CVC insertion. Extravasation of norepinephrine occurred in 35 patients (75.8 events/1,000 d of PIVC infusion [95% CI, 52.8-105.4 events/1,000 d of PIVC infusion]). Most extravasations caused no or minimal tissue injury. No patient required surgical intervention. INTERPRETATION: This study suggests that implementing a protocol for peripheral administration of norepinephrine safely can avoid 1 CVC day in the average patient, with 51.6% of patients not requiring CVC insertion. No patient experienced significant ischemic tissue injury with the protocol used. These data support performance of a randomized, prospective, multicenter study to characterize the net benefits of peripheral norepinephrine administration compared with norepinephrine administration through a CVC.

Monocarboxylate transporters facilitate succinate uptake into brown adipocytes.

Uptake of circulating succinate by brown adipose tissue (BAT) and beige fat elevates whole body energy expenditure, counteracts obesity, and antagonizes systemic tissue inflammation in mice. The plasma membrane transporters that facilitate succinate uptake in these adipocytes remain undefined. Here we elucidate a mechanism underlying succinate import into BAT via monocarboxylate transporters (MCTs). We show that succinate transport is strongly dependent on the proportion of it present in the monocarboxylate form. MCTs facilitate monocarboxylate succinate uptake, which is promoted by alkalinization of the cytosol driven by adrenoreceptor stimulation. In brown adipocytes, we show that MCT1 primarily facilitates succinate import, however other members of the MCT family can partially compensate and fulfill this role in the absence of MCT1. In mice, we show that acute pharmacological inhibition of MCT1 and 2 decreases succinate uptake into BAT. Conversely, congenital genetic depletion of MCT1 alone has little effect on BAT succinate uptake, indicative of additional transport mechanisms with high capacity in vivo . In sum, we define a mechanism of succinate uptake in BAT that underlies its protective activity in mouse models of metabolic disease.

Lactate regulates cell cycle by remodelling the anaphase promoting complex.

Lactate is abundant in rapidly dividing cells owing to the requirement for elevated glucose catabolism to support proliferation1-6. However, it is not known whether accumulated lactate affects the proliferative state. Here we use a systematic approach to determine lactate-dependent regulation of proteins across the human proteome. From these data, we identify a mechanism of cell cycle regulation whereby accumulated lactate remodels the anaphase promoting complex (APC/C). Remodelling of APC/C in this way is caused by direct inhibition of the SUMO protease SENP1 by lactate. We find that accumulated lactate binds and inhibits SENP1 by forming a complex with zinc in the SENP1 active site. SENP1 inhibition by lactate stabilizes SUMOylation of two residues on APC4, which drives UBE2C binding to APC/C. This direct regulation of APC/C by lactate stimulates timed degradation of cell cycle proteins, and efficient mitotic exit in proliferative human cells. This mechanism is initiated upon mitotic entry when lactate abundance reaches its apex. In this way, accumulation of lactate communicates the consequences of a nutrient-replete growth phase to stimulate timed opening of APC/C, cell division and proliferation. Conversely, persistent accumulation of lactate drives aberrant APC/C remodelling and can overcome anti-mitotic pharmacology via mitotic slippage. In sum, we define a biochemical mechanism through which lactate directly regulates protein function to control the cell cycle and proliferation.

Isolation of extracellular fluids reveals novel secreted bioactive proteins from muscle and fat tissues.

Proteins are secreted from cells to send information to neighboring cells or distant tissues. Because of the highly integrated nature of energy balance systems, there has been particular interest in myokines and adipokines. These are challenging to study through proteomics because serum or plasma contains highly abundant proteins that limit the detection of proteins with lower abundance. We show here that extracellular fluid (EF) from muscle and fat tissues of mice shows a different protein composition than either serum or tissues. Mass spectrometry analyses of EFs from mice with physiological perturbations, like exercise or cold exposure, allowed the quantification of many potentially novel myokines and adipokines. Using this approach, we identify prosaposin as a secreted product of muscle and fat. Prosaposin expression stimulates thermogenic gene expression and induces mitochondrial respiration in primary fat cells. These studies together illustrate the utility of EF isolation as a discovery tool for adipokines and myokines.

Architecture of the outbred brown fat proteome defines regulators of metabolic physiology.

Brown adipose tissue (BAT) regulates metabolic physiology. However, nearly all mechanistic studies of BAT protein function occur in a single inbred mouse strain, which has limited the understanding of generalizable mechanisms of BAT regulation over physiology. Here, we perform deep quantitative proteomics of BAT across a cohort of 163 genetically defined diversity outbred mice, a model that parallels the genetic and phenotypic variation found in humans. We leverage this diversity to define the functional architecture of the outbred BAT proteome, comprising 10,479 proteins. We assign co-operative functions to 2,578 proteins, enabling systematic discovery of regulators of BAT. We also identify 638 proteins that correlate with protection from, or sensitivity to, at least one parameter of metabolic disease. We use these findings to uncover SFXN5, LETMD1, and ATP1A2 as modulators of BAT thermogenesis or adiposity, and provide OPABAT as a resource for understanding the conserved mechanisms of BAT regulation over metabolic physiology.

Retrospective evaluation of a delirium order set utilizing nonpharmacologic and pharmacologic interventions for the treatment of delirium in medical intensive care unit patients.

PURPOSE: To describe the use of a medical intensive care unit (MICU) delirium order set pilot and its associated impact on utilization of nonpharmacologic and pharmacologic interventions, pharmacologic continuation at transitions of care, and resolution of ICU delirium. METHODS: This was a retrospective cohort analysis of MICU patients who received delirium management using an order set pilot compared to standard care. Patients 18 years of age or older admitted to the MICU between May 2019 and January 2020 who received an antipsychotic or valproic acid for the treatment of delirium were included. RESULTS: Pharmacologic treatment continuation past ICU discharge occurred in 30% of patients in the pilot cohort (n = 50) compared to 54% of patients receiving standard care (n = 50; P = 0.027). On treatment days 1 through 7, utilization of deliriogenic medications was significantly lower in the pilot cohort (78% vs 96%, P = 0.007). No differences were observed between the groups in delirium resolution, delirium recurrence, hospital and ICU length of stay, or mortality. CONCLUSION: A MICU order set prioritizing nonpharmacologic management and limiting the duration of pharmacologic agents for delirium may aid providers in the management of ICU delirium and reduce exposure to pharmacologic interventions.

Association of Arterial pH With Hemodynamic Response to Vasopressin in Patients With Septic Shock: An Observational Cohort Study.

OBJECTIVES: Vasopressin is reported to retain vasoconstrictive activity in the setting of acidemia, but preclinical models are inconsistent and studies have not evaluated the clinical effectiveness of vasopressin based on arterial pH. This study sought to determine the association between arterial pH and blood pressure after vasopressin initiation in septic shock. DESIGN: This retrospective, multicenter, observational cohort study evaluated the association of arterial pH at the time of vasopressin initiation with hemodynamic response to vasopressin and change in catecholamine dose after vasopressin initiation. Hemodynamic response was defined as a catecholamine dose decrease with mean arterial pressure greater than or equal to 65 mm Hg at 6 hours after vasopressin initiation. SETTING: Patients from eight hospitals in a health system were evaluated. PATIENTS: Patients with septic shock initiated on vasopressin as a catecholamine adjunct between January 2012 and November 2017 were screened for inclusion. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: A total of 1,350 patients were included. At the time of vasopressin initiation patients were severely ill with arterial pH 7.28 ± 0.13, Sequential Organ Failure Assessment 14.1 ± 3.5, lactate 5.6 ± 4.6 mmol/L, and norepinephrine-equivalent catecholamine dose 32.3 ± 25.4 µg/min. After adjusting for lactate and Sequential Organ Failure Assessment with multivariable logistic regression, lower arterial pH was independently associated with lower odds of hemodynamic response to vasopressin (for each 0.1 unit arterial pH was below 7.40, response odds ratio 0.79; 95% CI, 0.72-0.87). For each 0.1 unit the pH was below 7.40 at vasopressin initiation, the norepinephrine-equivalent catecholamine dose increased by 1.5 µg/min (95% CI, 0.5-2.5 µg/min) at 1 hour, and increased by 2.5 µg/min (95% CI, 1.4-3.5 µg/min) at 6 hours after vasopressin initiation. CONCLUSIONS: Compared with higher arterial pH, patients with septic shock and low arterial pH had lower odds of vasopressin response and higher catecholamine doses after vasopressin initiation. Similar to other vasopressors, the clinical effectiveness of vasopressin appears to be impaired in the setting of acidemia.

Hemodynamic Response to Vasopressin Dosage of 0.03 Units/Min vs. 0.04 Units/Min in Patients With Septic Shock.

BACKGROUND: Arginine vasopressin (AVP) is suggested as an adjunct to norepinephrine in patients with septic shock. Guidelines recommend an AVP dosage up to 0.03 units/min, but 0.04 units/min is commonly used in practice based on initial studies. This study was designed to compare the incidence of hemodynamic response between initial fixed-dosage AVP 0.03 units/min and AVP 0.04 units/min. METHODS: This retrospective, multi-hospital health system, cohort study included adult patients with septic shock receiving AVP as an adjunct to catecholamine vasopressors. Patients were excluded if they received an initial dosage other than 0.03 units/min or 0.04 units/min, or AVP was titrated within the first 6 hours of therapy. The primary outcome was hemodynamic response, defined as a mean arterial pressure ≥65 mm Hg and a decrease in catecholamine dosage at 6 hours after AVP initiation. Inverse probability of treatment weighting (IPTW) based on the propensity score for initial AVP dosage receipt was utilized to estimate adjusted exposure effects. RESULTS: Of the 1536 patients included in the observed data, there was a nearly even split between initial AVP dosage of 0.03 units/min (n = 842 [54.8%]) and 0.04 units/min (n = 694 [45.2%]). Observed patients receiving AVP 0.03 units/min were more frequently treated at the main campus academic medical center (96.3% vs. 52.2%, p < 0.01) and in a medical intensive care unit (87.4% vs. 39.8%, p < 0.01). The IPTW analysis included 1379 patients with achievement of baseline covariate balance. There was no evidence for a difference between groups in the incidence of hemodynamic response (0.03 units/min 50.0% vs. 0.04 units/min 53.1%, adjusted relative risk 1.06 [95% CI 0.94, 1.20]). CONCLUSIONS: Initial AVP dosing varied by hospital and unit type. Although commonly used, an initial AVP dosage of 0.04 units/min was not associated with a higher incidence of early hemodynamic response to AVP in patients with septic shock.

Safety of bedside placement of tunneled dialysis catheter in COVID-19 patients.

COVID-19 patients admitted to the ICU have high incidence of AKI requiring prolonged renal replacement therapy and often necessitate the placement of a tunneled dialysis catheter (TDC). We describe our experience with two cases of COVID-19 patients who underwent successful bedside placement of TDC under ultrasound guidance using anatomical landmarks without fluoroscopy guidance. Tunneled dialysis catheter placement under direct fluoroscopy remains the standard of care; but in well selected patients, placement of tunneled dialysis catheter at the bedside using anatomic landmarks without fluoroscopy can be safely and successfully performed without compromising the quality of care and avoid transfer of COVID-19 infected patients outside the ICU.

Effectiveness and Safety of Twice Daily Versus Thrice Daily Subcutaneous Unfractionated Heparin for Venous Thromboembolism Prophylaxis at a Tertiary Medical Center.

BACKGROUND: The direct comparison of twice daily (BID) and thrice daily (TID) dosing of subcutaneous low dose unfractionated heparin (LDUH) for venous thromboembolism (VTE) prophylaxis in a mixed inpatient population is not well-studied. OBJECTIVE: This study evaluated the effectiveness and safety of BID compared to TID dosing of LDUH for prevention of VTE. METHODS: Retrospective, single-center analysis of patients who received LDUH for VTE prophylaxis between July and September 2015. Outcomes were identified by ICD-9 codes. A matched cohort was created using propensity scores and multivariate analysis was conducted to identify independent risk factors for VTE. The primary outcome was incidence of symptomatic VTE. RESULTS: In the full cohort, VTE occurred in 0.71% of patients who received LDUH BID compared to 0.77% of patients who received LDUH TID (p = 0.85). There was no difference in major (p = 0.85) and minor (p = 0.52) bleeding between the BID and TID groups. For the matched cohort, VTE occurred in 1.4% of BID patients and 2.1% of TID patients (p = 0.32). Major bleed occurred in 0.36% of BID patients and 0.52% of TID patients (p = 0.7), while a minor bleed was seen in 3.4% of BID patients and 2.1% of TID patients (p = 0.13). Personal history of VTE (p = 0.002) and weight (p = 0.035) were independently associated with increased risk of VTE. CONCLUSION: This study did not demonstrate a difference in effectiveness or safety between BID and TID dosing of LDUH for VTE prevention.

Association of Catecholamine Dose, Lactate, and Shock Duration at Vasopressin Initiation With Mortality in Patients With Septic Shock.

OBJECTIVES: To determine the association of catecholamine dose, lactate concentration, and timing from shock onset at vasopressin initiation with in-hospital mortality. DESIGN: Retrospective, observational study using segmented and multivariable logistic regression to evaluate the associations of catecholamine dose, lactate concentration, and timing from shock onset at vasopressin initiation with in-hospital mortality. SETTING: Multiple hospitals within the Cleveland Clinic Health System. PATIENTS: Adult patients who met criteria for septic shock based on the U.S. Centers for Disease Control and Prevention Adult Sepsis Event definition. INTERVENTIONS: All patients received continuous infusion vasopressin as an adjunct to catecholamine vasopressors. MEASUREMENTS AND MAIN RESULTS: In total, 1,610 patients were included with a mean Acute Physiology and Chronic Health Evaluation III 109.0 ± 35.1 and Sequential Organ Failure Assessment 14.0 ± 3.5; 41% of patients survived the hospital admission. At the time of vasopressin initiation, patients had median (interquartile range) lactate concentration 3.9 mmol/L (2.3-7.2 mmol/L), norepinephrine-equivalent dose 25 µg/min (18-40 µg/min), and 5.3 hours (2.1-12.2 hr) elapsed since shock onset. The odds of in-hospital mortality increased 20.7% for every 10 µg/min increase in norepinephrine-equivalent dose up to 60 µg/min at the time of vasopressin initiation (adjusted odds ratio, 1.21 [95% CI, 1.09-1.34]), but no association was detected when the norepinephrine-equivalent dose exceeded 60 µg/min (adjusted odds ratio, 0.96 [95% CI, 0.84-1.10]). There was a significant interaction between timing of vasopressin initiation and lactate concentration (p = 0.02) for the association with in-hospital mortality. A linear association between increasing in-hospital mortality was detected for increasing lactate concentration at the time of vasopressin initiation, but no association was detected for time elapsed from shock onset. CONCLUSIONS: Higher norepinephrine-equivalent dose at vasopressin initiation and higher lactate concentration at vasopressin initiation were each associated higher in-hospital mortality in patients with septic shock who received vasopressin.

Glucose metabolism and pyruvate carboxylase enhance glutathione synthesis and restrict oxidative stress in pancreatic islets.

Glucose metabolism modulates the islet ß cell responses to diabetogenic stress, including inflammation. Here, we probed the metabolic mechanisms that underlie the protective effect of glucose in inflammation by interrogating the metabolite profiles of primary islets from human donors and identified de novo glutathione synthesis as a prominent glucose-driven pro-survival pathway. We find that pyruvate carboxylase is required for glutathione synthesis in islets and promotes their antioxidant capacity to counter inflammation and nitrosative stress. Loss- and gain-of-function studies indicate that pyruvate carboxylase is necessary and sufficient to mediate the metabolic input from glucose into glutathione synthesis and the oxidative stress response. Altered redox metabolism and cellular capacity to replenish glutathione pools are relevant in multiple pathologies beyond obesity and diabetes. Our findings reveal a direct interplay between glucose metabolism and glutathione biosynthesis via pyruvate carboxylase. This metabolic axis may also have implications in other settings where sustaining glutathione is essential.

UCP1 governs liver extracellular succinate and inflammatory pathogenesis.

Non-alcoholic fatty liver disease (NAFLD), the most prevalent liver pathology worldwide, is intimately linked with obesity and type 2 diabetes. Liver inflammation is a hallmark of NAFLD and is thought to contribute to tissue fibrosis and disease pathogenesis. Uncoupling protein 1 (UCP1) is exclusively expressed in brown and beige adipocytes, and has been extensively studied for its capacity to elevate thermogenesis and reverse obesity. Here we identify an endocrine pathway regulated by UCP1 that antagonizes liver inflammation and pathology, independent of effects on obesity. We show that, without UCP1, brown and beige fat exhibit a diminished capacity to clear succinate from the circulation. Moreover, UCP1KO mice exhibit elevated extracellular succinate in liver tissue that drives inflammation through ligation of its cognate receptor succinate receptor 1 (SUCNR1) in liver-resident stellate cell and macrophage populations. Conversely, increasing brown and beige adipocyte content in mice antagonizes SUCNR1-dependent inflammatory signalling in the liver. We show that this UCP1-succinate-SUCNR1 axis is necessary to regulate liver immune cell infiltration and pathology, and systemic glucose intolerance in an obesogenic environment. As such, the therapeutic use of brown and beige adipocytes and UCP1 extends beyond thermogenesis and may be leveraged to antagonize NAFLD and SUCNR1-dependent liver inflammation.

Reinfection Rates Among Patients Who Previously Tested Positive for Coronavirus Disease 2019: A Retrospective Cohort Study.

BACKGROUND: Protection afforded from prior disease among patients with coronavirus disease 2019 (COVID-19) infection is unknown. If infection provides substantial long-lasting immunity, it may be appropriate to reconsider vaccination distribution. METHODS: This retrospective cohort study of 1 health system included 150 325 patients tested for COVID-19 infection via polymerase chain reaction from 12 March 2020 to 30 August 2020. Testing performed up to 24 February 2021 in these patients was included. The main outcome was reinfection, defined as infection ≥90 days after initial testing. Secondary outcomes were symptomatic infection and protection of prior infection against reinfection. RESULTS: Of 150 325 patients, 8845 (5.9%) tested positive and 141 480 (94.1%) tested negative before 30 August. A total of 1278 (14.4%) positive patients were retested after 90 days, and 62 had possible reinfection. Of those, 31 (50%) were symptomatic. Of those with initial negative testing, 5449 (3.9%) were subsequently positive and 3191 of those (58.5%) were symptomatic. Protection offered from prior infection was 81.8% (95% confidence interval [CI], 76.6-85.8) and against symptomatic infection was 84.5% (95% CI, 77.9-89.1). This protection increased over time. CONCLUSIONS: Prior infection in patients with COVID-19 was highly protective against reinfection and symptomatic disease. This protection increased over time, suggesting that viral shedding or ongoing immune response may persist beyond 90 days and may not represent true reinfection. As vaccine supply is limited, patients with known history of COVID-19 could delay early vaccination to allow for the most vulnerable to access the vaccine and slow transmission.

Choosing Wisely For Critical Care: The Next Five.

OBJECTIVES: To formulate new "Choosing Wisely" for Critical Care recommendations that identify best practices to avoid waste and promote value while providing critical care. DATA SOURCES: Semistructured narrative literature review and quantitative survey assessments. STUDY SELECTION: English language publications that examined critical care practices in relation to reducing cost or waste. DATA EXTRACTION: Practices assessed to add no value to critical care were grouped by category. Taskforce assessment, modified Delphi consensus building, and quantitative survey analysis identified eight novel recommendations to avoid wasteful critical care practices. These were submitted to the Society of Critical Care Medicine membership for evaluation and ranking. DATA SYNTHESIS: Results from the quantitative Society of Critical Care Medicine membership survey identified the top scoring five of eight recommendations. These five highest ranked recommendations established Society of Critical Care Medicine's Next Five "Choosing" Wisely for Critical Care practices. CONCLUSIONS: Five new recommendations to reduce waste and enhance value in the practice of critical care address invasive devices, proactive liberation from mechanical ventilation, antibiotic stewardship, early mobilization, and providing goal-concordant care. These recommendations supplement the initial critical care recommendations from the "Choosing Wisely" campaign.

Home testing for COVID-19: Benefits and limitations.

The home test kits for detecting SARS-CoV-2 infection with Food and Drug Administration emergency use authorization primarily use either isothermal nucleic acid amplification or antigen detection, and each test has advantages and limitations in terms of sensitivity and specificity, cost, results reporting, and results turnaround time. In clinical studies, these tests provide accurate positive results in symptomatic individuals, although negative results are less accurate. There are also accuracy concerns for positive results in asymptomatic individuals. These factors have implications for their clinical interpretation and use.

Effect of Phenylephrine Push Before Continuous Infusion Norepinephrine in Patients With Septic Shock.

BACKGROUND: IV pushes of phenylephrine may be used for patients with septic shock with the intent of rapidly achieving mean arterial pressure (MAP) goals. However, the clinical effectiveness and safety of this approach are unclear. RESEARCH QUESTION: In patients with septic shock, is administration of a phenylephrine push before norepinephrine initiation associated with a higher incidence of hemodynamic stability? METHODS: This retrospective, multicenter cohort study included adult patients with septic shock initiated on norepinephrine. Propensity scores for initial phenylephrine push receipt were generated, and patients receiving an initial phenylephrine push were propensity score-matched 1:2 to those not receiving an initial phenylephrine push. The primary outcome was achievement of hemodynamic stability (defined as maintaining MAP of ≥ 65 mm Hg for at least 6 h without an increase in continuous infusion vasoactive agent dosage) within 3 and 12 h of norepinephrine initiation. RESULTS: Of 1,317 included patients, 181 received an initial phenylephrine push; 141 phenylephrine push patients were matched to 282 patients not receiving a phenylephrine push. More patients who received a phenylephrine push achieved hemodynamic stability at hour 3 than those who did not receive a phenylephrine push (28.4% vs 18.8%; risk difference, 10%; 95% CI, 0.9%-18%). Phenylephrine push receipt was associated independently with hemodynamic stability within 3 h (adjusted OR, 1.8; 95% CI, 1.09-2.97), but not at 12 h (adjusted OR, 1.42; 95% CI, 0.93-2.16). Phenylephrine push receipt was associated independently with higher ICU mortality (adjusted OR, 1.88; 95% CI, 1.1-3.21). INTERPRETATION: Phenylephrine pushes were associated with a higher incidence of early, but not sustained, hemodynamic stability and were associated independently with higher ICU mortality. Caution is warranted when clinicians are considering the use of phenylephrine pushes in patients with septic shock.